Method for reducing amine based contaminants

ABSTRACT

Method for reducing resist poisoning. The method includes the steps of forming a first structure in a dielectric on a substrate, reducing amine related contaminants from the dielectric and the substrate prior to a formation of a second structure on the substrate such that the amine related contaminates will not diffuse out from either the substrate or the dielectric, wherein the reducing utilizes a plasma treatment which one of chemically ties up the amine related contaminates and binds, traps, or consumes the amine related contaminates during subsequent processing steps, forming the second structure on the substrate, and after the forming of the first structure, preventing poisoning of a resist layer in subsequent processing by the reducing.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/537,378, filed on Sep. 29, 2006, which is a continuation ofU.S. patent application Ser. No. 10/605,926, filed on Nov. 6, 2003, thedisclosures of which are expressly incorporated by reference herein intheir entirety. This application also claims priority to U.S.Provisional Application No. 60/429,828, filed on Nov. 27, 2002, which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention generally relates a semiconductor device and method ofmanufacture and, more particularly, to a semiconductor device and methodof manufacture which reduces the occurrence of resist poisoning.

BACKGROUND

To fabricate microelectronic semiconductor devices such as an integratedcircuit (IC), many different layers of metal and insulation areselectively deposited on a silicon wafer. The insulation layers may be,for example, silicon dioxide, silicon oxynitride, fluorinated silicateglass (FSG), carbon doped, silicon dioxide or organosilicad glass (OSG)and the like. These insulation layers are deposited between the metallayers, i.e., intermetal dielectric (IMD) layers, and may act aselectrical insulation therebetween or serve other known functions. Theselayers are typically deposited by any well known method such as, forexample, plasma enhanced chemical vapor deposition (PECVD), chemicalvapor deposition (CVD) or other processes.

The metal layers are interconnected by metallization through vias etchedin the intervening insulation layers. To accomplish this, the stackedlayers of metal and insulation undergo photolithographic processing toprovide a pattern consistent with a predetermined IC design. By way ofexample, the top layer may be covered with a photo resist layer ofphoto-reactive polymeric material for patterning via a mask. Aphotolithographic process using either visible or ultraviolet light isthen directed through the mask onto the photo resist layer to expose itin the mask pattern. An antireflective coating (ARC) layer such as PECVDSiON or spin on coating materials may be provided at the top portion ofthe wafer substrate to minimize reflection of light back to the photoresist layer for more uniform processing. The spin on ARCs may includeAR-1 4™ (manufactured by Shipley Company, LLC of Marlborough, Mass.) orsacrificial light absorbing material (hereinafter referred generally asSLAM).

To form vias, for example, etching may be used to connect the metallayers deposited above and below the insulation or dielectric layers.The etching may be performed by anisotropic or isotropic etching as wellas wet or dry etching, i.e., RIE (reactive ion etching), depending onthe physical and chemical characteristics of the materials. To maximizethe integration of the device components in very large scale integration(VLSI), it is necessary to increase the density of the components. Thisrequires very strict tolerances in the etching and photolithographicprocesses.

However, it is known that resist poisoning can occur during thephotolithographic processes. One example of resist poisoning during thelithographic process is caused by amine-induced poisoning of chemicallyamplified resists created during the patterning step. This may be causedwhen low k dielectrics are used for the IMD and interlevel dielectric(ILD). In a more general example, during the photolithographic process,contaminants that are incompatible with the photo-reactive polymericmaterial can migrate into the photo resist layer from the deposited filmon the wafer, itself. These contaminants then poison the photo resistlayer, which may result in a non-uniformity of the reaction byextraneous chemical interaction with the polymeric material. The resistpoisoning also may result in poor resist sidewall profiles, resistscumming and large CD variations. This leads to the formation of a photoresist footing or pinching, depending on whether a positive negative orphoto resist, respectively, is used during the process. This may alsolead to an imperfect transfer of the photo resist pattern to theunderlying layer or layers thus limiting the minimum spatial resolutionof the IC.

One known method to solving this problem is to run a totally freenitrogen or nitrogen containing molecule free process. Examples ofnitrogen containing molecules include N₂, NH₃, NO, NO₂, etc. However,all released FSG films are known to require either N₂O (silane films) orN₂ (TEOS) films. In addition, silicon nitride or silicon carbon nitrideis commonly employed as a copper cap under the IMD due to its superiorelectromigration performance as compared to silicon carbide. Finally,even if totally nitrogen free films are used, nitrogen from the ambientair, ARC/photoresist or nitrogen impurities contained in the depositionor etch gases can result in the presence of amines.

SUMMARY

In a first aspect of the invention, a method for reducing resistpoisoning is provided. The method includes forming a first structuresuch as, for example, a trench or via in a dielectric on a substrate andreducing amine related contaminants from the dielectric and thesubstrate created after the formation of the first structure. The methodfurther includes forming a second structure in the dielectric.

In another aspect of the invention, the first structure such as, forexample, a trench or via in a dielectric on a substrate. A first organicfilm is formed on the substrate which is then heated and removed fromthe substrate. A second organic film is formed on the substrate andpatterned to define a second structure in the dielectric.

In yet another aspect of the invention, a method for reducing resistpoisoning includes forming a first structure such as, for example, atrench or via in a dielectric on a substrate and performing DHF wet etchwith an approximate ratio of 100:1 on the dielectric. An anti-reflectivecoating (ARC) is formed on and then removed from the dielectric and thesubstrate. A second organic film is then formed on the substrate andpatterning of the second organic film is performed to define a secondstructure in the dielectric.

In still another aspect of the invention, the first structure is formedin a dielectric on a substrate. A wet etching is provided on the formedfirst structure at approximately 3 nm 100:1 ratio of DHF. An organicfilm is applied on the exposed portions of the first structure, thedielectric and the substrate. The applying step includes spin coating ofthe organic film on the exposed portions, baking the organic film atapproximately 100 degrees Celsius to 250 degrees Celsius and removingthe organic film by dry stripping or plasma etching. The structure thusformed is then capped and a second organic film is formed on thesubstrate and patterned to define a second structure in the dielectric.

In an aspect of the invention, the structure is embedded in thedielectric with a vertical dielectric adjacent to a vertical sidewall ofthe structure. The vertical dielectric is deposited after the patterningand etching of a structure into the dielectric. The dielectric includesone of SiO₂, F-doped SiO₂, and CH₃-doped SiO₂. The vertical dielectricincludes one of SiO₂, P-doped SiO₂, F-doped SiO₂, B-doped SiO₂, and B-and P-doped SiO₂.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 a through 1 e represent a typical fabrication technique forforming a layered structure using standard reactive ion etching (RIE)technique;

FIG. 2 represents a first aspect of the invention;

FIGS. 3 a through 3 c represent another aspect of the invention;

FIGS. 4 a through 4 d represent another aspect of the invention;

FIGS. 5 a through 5 d show a trough lithographic process aftercontaminants are constrained, bound or capped in lower layers;

FIG. 6 a is a representation of a top view of a device using the methodsof the invention;

FIG. 6 b is a representation of a cross sectional side view of a deviceusing methods of the invention; and

FIG. 7 shows an embodiment of the structure of the invention.

DETAILED DESCRIPTION

This invention is directed to a semiconductor device and method ofmanufacture and, more particularly, to a semiconductor device and methodof manufacture which reduces the occurrence of resist poisoning in thedevice. By reducing poisoning effects, the invention also significantlyreduces photo resist footing or pinching, depending on the use of apositive negative or photo resist, respectively. The reduction of thepoisoning allows for the fabrication of more densely packed integratedcircuits (IC) with better resolution of interconnects and the likethereon. This, in turn, results in a superior performance of the IC. Theformation of vias and troughs can be characterized as either a firststructure or a second structure, depending on the architecture of thedevice.

FIGS. 1 a through 1 e represent a typical fabrication technique forforming a layered structure using standard reactive ion etching (RIE)technique. The RIE process should be well understood by those ofordinary skill in the art and is not discussed in great detail herein.In the schematics, a multilayer arrangement on a semiconductorsubstrate, which is typically a silicon substrate, is shown. Thesubstrate may equally represent any type of film having knowncontaminants such as amines, for example.

FIG. 1 a shows a target layer 12 such as an oxide layer deposited on thesubstrate 10. In one embodiment, the oxide layer is approximately 8000Å. Any known photo-resist or ARC/photo-resist 14 is then deposited onthe oxide layer. FIG. 1 b represents a photolithographic processperformed on the photo-resist layer 14. In this representation, thephoto-resist layer 14 is exposed to light through a mask 16 to form animage on the photo-resist layer 14. Once the exposure is complete, theexposed photo-resist layer 14 is developed in order to remove thoseportions of the exposed photo-resist. This is typically performed by awet develop process using, for example, TMAH, as known in the art. Theresulting pattern is shown in FIG. 1 c.

A reactive ion etching is then performed on the target layer 12 in orderto form a first structure such as a via 16, for example (FIG. 1 d). Thefirst structure may equally be a wire trough, in some applications. Theremaining portions of the photo-resist layer 14 are then removed by, forexample, dry strip techniques (FIG. 1 e) using, for example, O₂, H₂, N₂,plasmas or damascene plasmas, all known in the art. In one embodiment,the first structure (i.e., a via) is at a depth of about 7500 Å. Itshould be well understood by those of ordinary skill in the art, though,that other depths are also contemplated by the invention. At the end ofthis process, contaminants are known to be associated with the substrate10 or target layer 12 basically due to the etching process, to thisstage.

FIG. 2 is representative of a first embodiment of the invention. In FIG.2, the structure of FIG. 1 e is subjected to a plasma wafer treatment.In one embodiment, the plasma wafer treatment is an N₂O plasma treatmentperformed at approximately 400 degrees Celsius. In one aspect, the N₂Owill chemically tie up the contaminants such that the contaminants willnot diffuse out from either the substrate layer 10 or the target layer12, i.e., oxide layer. In another aspect, it is assumed that the N₂Opassivates the exposed layer in order to bind, trap or consume thecontaminants such that amine, for example, will not diffuse out from theexposed layers during subsequent etching processes. In either scenario,it is known that the plasma wafer treatment of the invention preventspoisoning of the resist layer in subsequent processing steps. Analternative embodiment uses a N₂O, O₂ or H₂ plasma with no deposition inorder to achieve the same effect. The time for the N₂O, O₂ or H₂ plasmamay be from one to 60 seconds, for example, alternative, the wafer maybe baked for approximately 0.1 to 10 minutes at 400 degrees Celsius topartially outgas amines.

FIGS. 3 a through 3 c represent another aspect of the invention. In FIG.3 a, an optional wet etching of approximately 30 seconds at 25 degreesCelsius, 100:1 ratio of DHF (dilute hydrofluoric acid) is performed onthe device of FIG. 1 e. It should be recognized by those of ordinaryskill in the art that other ratios, times or temperatures of the DHF mayalso be used in accordance with the principles of the invention. In FIG.3 b, an organic film such as an antireflective coating 18 (ARC) isapplied to the device of FIG. 1 e, with or without the optional wetetching being performed. In one aspect, the ARC is spin coated onto theentire exposed surfaces of the target layer 12 and the substrate 10. TheARC is then baked at approximately 100 degrees Celsius to 250 degreesCelsius and more preferably between 150 degrees Celsius to 220 degreesCelsius in order to diffuse the amine based contaminants into the ARC.The ARC is removed by dry stripping or plasma etching, similar to thatdescribed above with reference to the photo-resist layer 14. This latterstep is shown in FIG. 3 c. The ARC may be exposed to UV light.

FIGS. 4 a through 4 d represent another aspect of the invention. FIGS. 4a through 4 c are substantially identical to those steps shown anddescribed with reference to FIGS. 3 a through 3 c, and are not describedagain. FIG. 4 d shows the deposition of a thin plasma cap 20. The cap 20can be deposited by any known method such as, for example, PECVD,HDPCVD, SACVD, APCVD and the like at a temperature ranging from 25degrees Celsius to 500 degrees Celsius, and preferably at 400 degreesCelsius. In one aspect, the oxide cap 20 is approximately 25 nm;however, other thicknesses are also contemplated for implementation bythe invention. In one embodiment, prior to the deposition of the oxidecap, an annealing process is performed at about 400 degrees Celsius forabout 60 seconds. In another embodiment, prior to the deposition of theoxide layer, a N₂O or O₂ plasma etch at an approximate temperature of400 degrees Celsius is performed. (These steps may be represented byFIG. 4 c.) The silicon dioxide cap will seal any of the remaining aminebased contaminants in the layers 10 and 12. In the process describedwith reference to FIGS. 4 a-dc, any amine based contaminants will notdiffuse out during subsequent processing steps to contaminate theresulting device.

FIGS. 5 a through 5 d show a typical trough lithographic process afterthe contaminants such as, for example, amine based contaminants, areconstrained, bound or capped in the lower layers 10 and 12. This processwill now provide a second structure such as channels or troughs in thetarget layer 12, but without any contaminants from the resist or otherdevice layers contaminating the device during this further processingstage. In another aspect, the second structure may be a via. Inaccordance with the invention, more accurate troughs can be achieved,increasing the density of the device in addition to its performance.

In particular, FIG. 5 a shows a known photo-resist 20 deposited on theoxide layer 12. FIG. 5 b represents a photolithographic processperformed on the photo-resist layer 20. In this representation, thephoto-resist layer 20 is exposed to light through a mask 22 to formchannels or troughs in the photo-resist layer 20. Once the exposure iscomplete, the exposed photo-resist layer 20 is developed in order toremove those portions of the exposed photo-resist. The resulting patternis shown in FIG. 5 c. A reactive ion etching is then performed on thetarget layer 12 in order to form one or more channels 24, for example(FIG. 5 d). The remaining portions of the photo-resist layer 18 are thenremoved by, for example, dry strip techniques (FIG. 5 d) to form thechannels “C” of the final device structure.

It should be understood that the steps shown in FIG. 2, FIGS. 3 athrough 3 c or FIGS. 4 a through 4 d may be repeated if other structuresare to be formed on any overlaying layers. Likewise, in any multilayeredstructure, the steps shown and described herein may be repeated toreduce or eliminate contaminants during further processing. This ismainly due to the fact that more contaminants may have formed on ordiffused into the layers, now shown, or additionally formed layers dueto the use of additional resist layers and etching or other processingsteps.

Table 1, reproduced below, is representative of the advantages achievedby the aspects of the invention, compared to conventional methods. Thedata in Table 1 and table 2 were generated using duel damascene wiresand vias with 200 nm minimum critical dimension. In Table 1, it is shownthat a conventional method of fabrication yields approximately 15%non-defective devices (chips). In stark improvement, the use of theaspect of FIG. 2 shows a yield of 60% of non-defective devices (chips).Of even greater yield is the aspect of the invention of FIGS. 3 athrough 3 d which show a yield of 75% of non-defective devices (chips).The aspect of the invention of FIGS. 4 a through 4 d shows a yield of90% of non-defective devices (chips). This improvement over the standardfabrication processes is attributable to the elimination of contaminantsduring the fabrication processes.

TABLE 1 % chips with greater than 0 resist poisoning Process #lotsdefect yield Standard process 6 15% Added lithographic work 24 60% AddedDHF clean and 38 75% lithographic work Added DHF clean + 50 90% lithowork + thin oxide cap

Table 2 represents the critical dimension (CD) or diameter of the viausing either a 40 mJ or 70 mJ dose. As seen in Table 2, below, thestandard fabrication process, at 40 mJ, provides an approximate via sizeof 200 nm with “scummed” edges. That is, the edges of the via using thestandard fabrication process has resist that does not completely clearout thus resulting in blurred edges. In stark contrast, the aspects ofthe invention result in vias with clearly defined edges. Additionally,the via are also larger due to the suppression of the poisoning.

TABLE 2 Process Via 40 mJ dose Via cd 70 mJ dose Standard Scummedapprox. 360 nm 200 nm 400C oxygen plasma 400 nm DHF + thin oxide cap 400nm 500 nm

In one embodiment, the formation of the via on the target layer is afirst structure and the formation of the trough is a second structure.The first and second structure, however, can be switched, depending onthe design of the device. In one aspect, the dimension of the firststructure is about 200 nm and the photolithographic exposure wavelengthis about 248 nm. Of course, those of ordinary skill in the art willreadily recognize that other dimensions and photographic minimums arealso contemplated by the invention and that the above example is onlyone illustrative embodiment of the invention.

FIG. 6 a shows a top view of an example of the device of the inventionwith both a first structure and a second structure. FIG. 6 b shows across sectional view of an example of the device of the invention. Theviews of FIGS. 6 a and 6 b are taken in a scanning electron microscopeof a dual damascene copper wire and via with resist poisoning.

It is contemplated by the invention that the SiO₂ thin oxide cap can bea sacrificial film (i.e., it is removed during the post via RIE clean,trough RIE, post trough RIE clean, or other steps). Alternatively, theSiO₂ thin oxide cap can remain on the wafer post-metallization, as shownin FIG. 7, layer 7, for example. More particularly, FIG. 7 shows dualdamascene wire 2 and via 3 contacting the previous metal level 4. Thewire 2 and via 3 are embedded in dielectric 1 and the wire 4 is embeddedin dielectric 6. An optional via RIE stop layer or copper diffusionbarrier 5 is deposited over dielectric layer 6 and wire 4. If the SiO₂thin oxide cap is not removed during processing, then it will remain onthe wafer as shown by layer 7.

In an aspect of the invention, the structure is embedded in thedielectric with a vertical dielectric adjacent to a vertical sidewall ofthe structure. The vertical dielectric is deposited after the patterningand etching of a structure into the dielectric. The dielectric includesone of SiO₂, F-doped SiO₂, and CH₃-doped SiO₂. The vertical dielectricincludes one of SiO₂, P-doped SiO₂, F-doped SiO₂, B-doped SiO₂, and B-and P-doped SiO₂.

While the invention has been described in terms of embodiments, thoseskilled in the art will recognize that the invention can be practicedwith modifications and in the spirit and scope of the appended claims.

1. A method for reducing resist poisoning comprising the steps of:forming a first trench in a dielectric layer on a substrate, wherein thetrench defines a portion of a surface of the substrate; forming a firstorganic film on and contacting the portion of the surface of thesubstrate defined by the trench; heating the first organic film;removing the first organic film from the substrate; forming aphotoresist on and contacting the portion of the surface of thesubstrate defined by the trench and on an upper surface of thedielectric layer, wherein the photoresist is formed after the firstorganic film is removed; patterning the photoresist; forming a secondtrench in the dielectric layer through the patterned photoresist.
 2. Themethod of claim 1, wherein the first organic film comprises ARC(anti-reflective coating).
 3. The method of claim 1, wherein the heatingstep comprises annealing at a temperature from about 100 to about 250degrees Celsius.
 4. The method of claim 1, wherein the removing stepcomprises a plasma etch.
 5. The method of claim 1, wherein before theforming of the first trench, performing a 100:1 DHF wet etch of thedielectric.
 6. The method of claim 1, wherein after the removing step,depositing a non-amine dielectric having a thickness of about 25 nm. 7.The method of claim 6, wherein the non-amine dielectric comprises oxide.8. The method of claim 6, wherein before the depositing step, performingan anneal at a temperature of about 400 degrees Celsius for about 60seconds.
 9. The method of claim 6, wherein before the depositing step,performing an N₂0 or 0₂ plasma etch at a temperature of about 400degrees Celsius.
 10. The method of claim 1, wherein after the heatingstep, exposing the first organic film to UV light.
 11. The method ofclaim 1, wherein the first structure comprises one of a via and atrough, and the second structure comprises one of a trough and a via.12. The method of claim 1, wherein a critical dimension of the firststructure is about 200 nm and the photolithographic minimum is about 248nm.
 13. The method of claim 1, wherein the first organic film and thephotoresist are formed on the portion of the surface of the substratedefined by the trench at different times.
 14. The method of claim 1,wherein: the forming the first organic film comprises forming the firstorganic film on the portion of the surface of the substrate defined bythe trench; the removing the first organic film comprises removing thefirst organic film from the portion of the surface of the substratedefined by the trench; and the forming the photoresist comprises formingthe defined by the trench on the portion of the surface of the substratedefined by the trench after the removing the first organic film.
 15. Amethod for reducing resist poisoning comprising the steps of: forming afirst structure in a dielectric on a substrate; performing a DHF wetetch on the dielectric at a ratio of about 100:1; forming ananti-reflective coating (ARC) on the dielectric and a portion of asurface of the substrate defined by the first structure; baking the ARCin order to diffuse amine based contaminants into the ARC; removing theARC after the baking the ARC; and forming a second organic film on theportion of the surface of the substrate defined by the first structureand patterning the second organic film to define a second structure inthe dielectric.
 16. The method of claim 15, further comprising the stepof forming an oxide cap on the dielectric and the substrate prior toforming the second organic film step.
 17. The method of claim 15,wherein the baking the ARC includes baking the ARC between approximately175 degrees Celsius to 220 degrees Celsius and dry step removal of theARC to eliminate amine based contaminants.
 18. The method of claim 15,wherein the ARC and the second organic film are formed at differenttimes on the same portion of the surface the substrate defined by thefirst structure.
 19. The method of claim 15, wherein the forming thesecond organic film comprises forming the second organic film on thesame portion of the surface the substrate from which the ARC wasremoved.